The TGF-ss superfamily is the largest group of secreted signaling molecules found in man. They regulate a very large number of cellular, developmental and physiological processes including early axial development, germ layer specification, gastrulation, organogenesis, and left right asymmetry. We will use a well-studied model organism (Drosophila) to elucidate general principles by which the activities of TGF-ss signaling pathways are regulated during development. In Aim 1 we will examine mechanisms by which three new gene products control Dpp signaling in the early embryo. These experiments will significantly improve our understanding of how extracellular factors, affect signaling dynamics of TGF-ss factors in vivo. In Aim 2 we will determine the functional significance and mechanism of TGF-ss type II receptor basolateral localization in epithelial cells using a combination of Drosophila molecular genetics and proteomics in MDCK cells. These experiments will considerably enhance our understanding of how receptors in this major signaling pathway are delivered to different sub-compartments of the cell membrane and how this affects tissue development. In Aim 3 we will use molecular genetics methods, to determine how one sub-family (Activins) influences the signaling output of another subfamily (BMPs) to control tissue growth. This work will determine whether cross TGF-ss- pathway signaling or non-canonical signaling contributes to growth regulation, an important issue in the development of many tissues and disease processes. Impact on human health: In humans, genetic and somatic mutations that alter the expression or regulation of TGF-ss factors are major contributors to numerous disease processes including cancer, metastasis, fibrosis, immune regulation, cardiovascular disease, and connective tissue disorders. Therefore, there is currently much effort within the medical community to develop therapeutic intervention strategies aimed at manipulating the activities of this pathway during treatment of various disease or injury situations. Our studies aimed at understanding how the activity of these factors is regulated in time and space in a model organism should aid in the identification of new therapeutic targets and/or development or more effective treatment protocols.